1. Field of the Invention
This invention relates to a one-part or commonly known as a "one-package" curable elastic sealant which contains as a main ingredient an acrylic isocyanate elastomer having free isocyanate groups in the molecule, and which is curable in the presence of the moisture in the air.
3. Description of the Prior Art
Sealants filling the joints of buildings and the like must have the elastic property which permits them to expand and contract according to dimensional variations in the building materials constituting the joints due to temperature changes. Moreover, they desirably do not contain materials such as water and organic solvents which scatter into the atmosphere or evaporate causing dimensional reductions in the fillings.
Frequently used polyacrylic sealants, generally, have superior weatherability, colorability and durability, but to data such sealants have been obtained only as noncrosslinked non-elastic emulsions or organic solvent solutions. Hence, such sealants cannot adjust to dimensional changes in the joint which may be caused by temperature changes, etc. Consequently, cracks or gaps tend to occur in the joints, and water, organic solvents, etc. scatter or evaporate into the air. As a result, the sealant shrinks with time, and does not perform adequately. For this reasons, the utility of such sealants is limited, and presently they are used only in ALC (Autoclaved Lightweight Concrete) boards and the like.
Many of elastic sealants now commercially available are two-part curable. That is the sealant is supplied to the user in two parts which must be mixed by the user prior to use. However, these two-part curable elastic sealants tend to exhibit poor adhesion and curing as a result of weighing errors, nonuniform mixing, etc. which occur during the mixing of the two packages. Moreover, once the two packages have been mixed, the mixture cannot be stored and any unused portion is wasted. Thus, the efficiency of this type of sealant is very poor.
A one-part curable sealant of the urethane type obtained by the polyaddition reaction between a polyisocyanate and a polyol such as polyethylene glycol is known which does not suffer from the drawbacks of the two-part curable sealant.